An integrated circuit chip of the type commonly used in electronic devices typically comprises several circuit functional blocks, each having many electronic components and at least one bond pad for the input and output of electronic signals. The integrated circuit chip is typically mounted on a leadframe, which has a plurality of electrical leads extending therefrom. Wire bonds connect each bond pad on the chip to at least one of the leads.
The integrated circuit chip and leadframe are encased in plastic to electrically and mechanically insulate the integrated circuit components from the outside world. Only the leads emerge from the plastic casing to allow the input and output of electronic signals to the integrated circuit chip.
The wire bonds connecting the bond pads to the leads are flexible, and must be prevented from contacting each other to avoid short-circuiting. The wire bonds must therefore be made as short as possible, so that the injection molding process which produces the plastic casing does not inadvertently push the wire bonds together. Likewise, the leads must be separated from each other by a minimum distance so as to prevent short-circuiting between the leads.
In addition to the foregoing design factors, integrated circuit chips have traditionally been designed with a square or rectangular shape. When rectangular shapes have been used, the ratio of the length of the chip to its width, known as the aspect ratio, has typically been limited to 3:1 or less. This was due to the common understanding that elongated shapes would be prone to breakage during the fabrication and packaging process.
The need for spacing between leads and between wire bonds results in a need to increase the perimeter length of the integrated circuit chip when a large number of leads are used. However, the squarish, low aspect ratio shapes used for integrated circuit chips result in relatively short perimeter lengths.
These competing considerations have, in many cases, resulted in integrated circuit chips being enlarged beyond the size strictly necessary to accommodate the circuit functional blocks contained therein. These enlarged integrated circuit chips have sufficient perimeter length to permit connection to a large number of leads. However, because semiconductor wafers are available at a fixed cost per unit area, the wasted space in an enlarged integrated circuit chip adds considerably to the cost of the integrated circuit chip package.